4. What happens to arsenic in the body?

4.1 What happens to arsenic absorbed by the body?

The amount of arsenic absorbed into the body from inhaled airborne particles is highly dependent on two factors, the size of particles and their solubility. The size of the particles determines how far into the lungs they can penetrate – the further they penetrate the more likely arsenic is to be absorbed. The solubility of the particles in the fluid lining the lungs determines how easily arsenic will be absorbed into the blood stream. In the gut, soluble arsenic compounds from food and beverages are rapidly and extensively absorbed into the blood stream.

In humans and most common laboratory animals, inorganic arsenic is metabolized via two main types of reaction: (1) conversion of the pentavalent form of arsenic - arsenate - to the trivalent form - arsenite, and (2) methylation, i.e. addition of a methyl group comprising one atom of carbon and three of hydrogen (-CH3) to the trivalent form. After methylation arsenic can be rapidly eliminated from the body with the urine. There can be large differences between individual humans in their capacity for methylation that is most likely due to differences in enzyme capacity in the body. It is not clear if children have a reduced capacity for methylation compared with adults. Studies suggest that the main pathway for getting rid of arsenic from the body, methylation, may be inhibited at high exposures.

4.2 What are the indicators of arsenic exposure?

The amounts of arsenic or its metabolites in blood, hair, nails and urine are used as indicators - biomarkers - of arsenic exposure. Blood arsenic is only useful for indicating either acute poisoning or repeated high-level exposures occurring over a long period. This is because arsenic rapidly disappears from blood.

Arsenic persists longer in hair and nails, which can, therefore, be used as indicators of past exposure. The concentration of arsenic, along a hair may be used to estimate the timing of an exposure.

The best estimate of recent exposure to inorganic arsenic is to measure it and its specific chemical metabolites in urine. However, consumption of certain seafood high in organic arsenic, such as seaweed or mollusks, produces one of the same metabolites as inorganic arsenic and may therefore exaggerate estimates of inorganic arsenic exposure in some people at certain times. Such foods should be avoided for 2–3 days before urine sampling. More...